In the 3rd Generation Partnership Project (3GPP), which is a standardization project for a mobile communication system, the introduction of terminal-to-terminal (Device to Device: D2D) communication is considered as a new function launched from the release 12 (refer to Non Patent Literature 1).
In D2D communication, a plurality of closely-located user terminals directly performs terminal-to-terminal communication not via a core network. On the other hand, in cellular communication, which is normal communication of a mobile communication system, a user terminal performs communication via a core network.
Meanwhile, for discovering a partner terminal of D2D communication, for example, a user terminal transmits a discovery signal used for discovering a user terminal near the user terminal. By receiving a response to the transmitted discovery signal, the user terminal can discover another user terminal that exists near itself. If the discovered other user terminal can perform D2D communication, the user terminal can perform D2D communication.